Method of forming and preparing tubular coil supports



July 24, 1956 w. F. STAHL 2,756,003

i z "L" li/HLTHD F FGRMlN G AND PREPARING TUBULAR COIL SUPPORTS William F. Stahl, Kenilworth, Ill.

Application August 25, 1953, Serial No. 376,438

8 Claims. (Cl. 242.-1)

This invention relates to Coil supports and, more particularly, to a method of forming and preparing tubular coil supports. The invention is especially useful in connection with the making of coils used in the electronics industry such as, for example, tuning coils, transformer coils, etc. wherein wire is wound upon a tubularsupport that is then equipped with an adjustable core for tuning the coil.

Tubes generally are Aformed by laminating strips of material one upon another in a spiral winding operation. ln this procedure a winding mandrel is provided and as the mandrel' is rotated the strips of material are drawn thereabout in spiral form and usually a plurality of strips are wound one upon another to formV a. sturdy tubular coil. 'This method is generally adopted'for the making of oeils or coil supports used in the electronics industry. The reason laminated tubes are preferred,y is that they are relatively cheap and, therefore, the cost of the'equipment in which they are used is considerably lessened. Where the tubes are used as coil supportsand the coils are equipped with, cores, which in many instances are movable-so that the electric properties of the coil can be varied as required, it is essential that the tube be dimensionally accurate so that free movement of the tuning core may be realized.

In winding a coil, wirev is drawn tightly about the tubular support. Since the wireis drawn taut the tubular support is frequently distorted when the Wire is drawn tightly thereabout. Even though itis readily possible to provide atube that is dimensionally accurate in the winding operation set out above,v still; when` they wire is drawn about the tube thetube. becomes distorted and the advantages of the dimensional accuracy completely disappear.

In order to overcome the effects of the distortionl that accompanies the wire winding operation, it. is Common fory tubes to be ordered that arel oversize and therefore even-though the wire is drawn tightly about the tube and distorts the same by forcing portions thereof inwardly, the interior dimensions of the tubular support are still large enough to enable the insertion of cores and the movement of adjustable cores. Whilethis practice enables electrical coils to be formedY that function satisfactorily, the practice is nevertheless wasteful in. that` it requires a larger amount of wirel to bezusedl inthe forming of each coil. The wire most,- frequently used isl copper, and copper wire isV quite expensive and` the extra length of wire used in each coil over. that. which would be required if the tubular support maintained its dimensional accuracy during the winding-operation, amounts. to many thousands of dollars a year for, each coil manu.- facturer.

it is accordingly an object4 of this invention to provide a method ofV forming and preparing a tubular coil support wherein the support remains undistorted after theY wire coil has been wound thereon. Another object of the invention is to providey aY coilforming method in whichv a pair' of matched man nited States Patent C) lice drels are employed, one beingused to form a dimensionally accurate tubular coilsupport thereon and the other being used to support the tube while a wire coil is wound thereon, the dimensions of the matched mandrels being related so that after the wire coil has been wound upon the tubular support, the support remains dimensionally accurate. A further'object of the invention is in the provision of a method of forming a coil wherein the tubular coil support remains dimensionallyy accurate during the coil winding operation, with the result that a support of precise size, may be employed and a savings in the wire costs realized. Yet a-further object is in the provision of a method as set out above, including the steps of winding a laminated tube upon afwinding mandrel and thereafter supporting the` tube on a support mandrel during the wire Winding operation, the dimensions of the mandrels being matched in a relationship whereby a push t is provided between the tube and: the support mandrel. Additional objects and advantages will appear as the specification proceeds.

An embodiment of the invention is illustrated in the accompanying drawing, in which:

Fig. l is a perspective view of a. tubularsupport equipped with end-.ilangesg Fig. 2 is. a broken perspective View or a winding mandreland in which the step of winding a laminated tube isbeingfcarriedjout; Fig. 3y is a transverse sectionalview of a winding mandrel with a tubular coil support thereon; Fig. 4 is a transverse sectional view of a tube after it has been; removedfrom the winding mandrel; Fig. 5 is a transverse'sectional view showing the tube being supported upon the support mandrel; Fig. 6 is a brokenV perspective viewshowing the step of winding a coil upon a supported tube; and Fig.y 7 is a diagrammatic view showinga support-and winding mandrell with specific dimensions applied thereto.

Fig. 2 will iin-st' be referred. to, since it illustrates the tirst step of forming a laminated tube. In this figure, a tubetorming or winding mandrel is indicated by the numeral It? and being drawn or wound about the mandrel ltis a strip ot material l1. While but a single strip 11 is illustrated in Fig. 2, it will be appreciated that any nurnber of strips may be employed in` forming the laminated tube. Actually, twolorthree stripsare usually provided and one is wound upon another to formL a multiple layer laminated tube. AnyA suitable material may be employed to provide the strip or strips 11 andfcustomarilyV a brous material is employed; Speci'cally, the strip- 1l may be formed of paper and it shouldbeY understood that the tube formed by this spirall winding. operationV may be subjected to later treatments such asy impregnation to form asturdy tubular support.

It is quitefpossible and now fairlyl common to form. a spirally-wound laminatedk tube wherein the dimensions thereof are quite accurate., Preferably, then, the tube formed by the spiral winding step illustrated in Fig. 2 is a dimensionally accuratetube., Since spirally winding laminatedV tubes is old andl well known inv the art, a detailed description more; elaborate than that. set out above willvnot be given, since' it is believed unnecessary to a complete understanding ofthe.- invention by those skilled inv the art. Similarly, forming laminated. tubes that are dimensionally accurate isalsoknown in the art, and` the precise apparatus and method employed tor achieving this result should. not then. be set. out in detail.

As shown inFig. 3', after the laminated tube has been formed upon the mandrel' 10, it is` seen that the walls of the tube cling fairly close to the walls of the mandrel. Actually, there is a slight bowing-outwardly o f the walls of the tube but it is practically imperceptible while the tube is uponA the mandrel 10`.v TheI bowing tendency, however, ismore pronounced# when the tube, whichr is designated-1y by the num'eralf- 12, isAv withdrawn from the mandrel. It is seen in Fig. 4 that each of the side walls of the tube 12 bow outwardly slightly.

After the tube 12 has been formed upon the mandrel it is withdrawn therefrom, which may be part of the winding operation, and it is then telescoped onto a support mandrel or coilwinding mandrel 13. The mandrel 13 is illustrated in Fig. 5. It is seen that when the tube 12 is telescoped onto the mandrel 13 that the side walls of the tube are straightened and the outward bowing thereof becomes very, very slight. lt is important to choose the dimensions of the mandrel 13 carefully so that the tube 12 is properly supported thereon and distortion of the tube thereby eliminated during the coilwinding operation.

After the tube 12 is properly supported upon the mandrel 13, an elongated wire 14 is wound upon the tube 13 to form the electric coil. The wire 14 may be formed of any suitable material and usually the wire is copper. The coil may be wound in any suitable manner and, for example, the support mandrel 13 may be rotated to draw and wind the wire 14 thereabout. Coilwinding operations are well known in the art and a detailed description of such winding operations is believed unnecessary herein.

A completed support for a coil is illustrated in Fig. l and shows the tube 12 having been cut into an appropriate length to form the coil support 15. The support 15 is equipped at each end with an end or terminal flange 16. Usually the flanges 16 are secured in position upon the tube 12 or the sectioned coil support 15 prior to the wire-winding operation, although other procedures may be followed if desired.

It has been found that if the dimensions of the winding mandrel 10 and the support mandrel 13 are correlated properly, that the tube 12 when the wire coil is wound thereabout, will not be distorted and that the formed coil may readily have a metallic core inserted therein and, specifically, the coil may be equipped with a movable iron core that will enable the coil to be properly tuned to meet the requirements of the particular circuit arrangement with which it is used. In order that the core move freely within the tube, it is essential that the inner dimensions of the tube be accurate throughout the length thereof. If the inner dimensions are smaller at certain points along the tubular support, the core cannot be inserted and if a movable core is employed the core cannot be moved beyond the point of obstruction. Tuning, then, is seriously limited. On the other hand, if the inner dimensions of the support are too great, a movable core will not be adequately held by friction at any point of adjustment therein and chances are quite great that a coil, though properly tuned initially, will not remain tuned especially if the apparatus is subjected to any vibration `which would cause movement of the adjusting core. It is fairly critical, then, that the dimensions of the tube used for the coil support remain quite accurate.

As has been brought out before, the customary practice has been to provide tubes 12 having greater dimensions than those actually required so that after the wire coil has been formed thereon the inner dimensions of the tubular support are still sucient to enable a movl able core to be employed therein and to be freely movJ able therein and not obstructed by areas of reduced di mensions. This is an extremely wasteful practice and it is therefore desirable to avoid the practice of ordering and using oversize tubes, if it is possible.

I have found that if the mandrel 13 used to support the tube 12 during the coilwinding operation is of such size that the tube 12 must be pushed onto the mandrel with a slight force during the telescoping operation, that the tube will then be properly supported and there will be no buckling and other distortion of the tube when the coil is wound thereon. Such a push lit can be obtained if the corners of the mandrel 13 snugly engage the corners of the tube 12, as is illustrated in Fig. 5. If this specific arrangement is provided, it is apparent that the tube 12 will be supported at each corner portion and the corners thereof cannot be buckled inwardly when the wire is drawn tightly thereagainst. At the same time, the snug engagement between the corners of the mandrel and corners of the tube tend to flatten the side walls of the tube and minimize the bowing outwardly thereof.

A specific example of the dimensions employed in a matched set of winding and support mandrels is shown in Fig. 7. Specifically, in this example the winding mandrel l? had side wall dimension of .515 inch while thc support mandrel 13 had side wall dimensions of .505 inch. The matched mandrels 10 and 13 with the dimensions indicated in Fig. 7 were used in forming the laminated tube 12 and in thereafter supporting the tube 12 during the coil-winding operation. It was found that the tube 12 formed on the mandrel 10 having wall dimensions of .515 inch was snugly received upon the support mandrel 13 having side wall dimensions of .505 inch, and that the tube 12 had to be pushed onto the mandrel 13 with sufficient force to overcome the frictional resistance tending to prevent the telescoping movement of the tube 12 and mandrel 13 and a push t between the two was thus provided.

When the coil was then Wound upon the tube and the tube subsequently withdrawn from the mandrel 13, it was found that there was no distortion of the tube and a core was readily inserted thereinto. The matched mandrels were employed for a considerable period of time for winding tubular coil supports and for supporting the tubes during the coil-winding operation, and it was found that the results in wire saving costs alone amounted to about $40,000 to $50,000 a year for this one coil manufacturer. It is apparent, then, that in providing matched mandrels, one of which is used in the tube-winding operation and the other of which is used in the coil-winding operation as a support for the tube, that when the mandrels are matched dimensionally so that a push tit is necessitated between the tube and support mandrel when the same are telescoped together, that the coil may the be formed upon this supported tube without the danger of distorting the walls of the tube and the inner dimensions thereof remain accurate. Thus it is not necessary to use oversize tubes as coil supports, and since many turns of wire are required to form each coil, the savings in costs are considerable.

While in the foregoing specification an embodiment of the invention has been set out in considerable detail for purposes of illustration, it will be apparent to those skilled in the art that considerable deviation from these details may be made without departing from the spirit and principles of the invention.

I claim:

1. In a method of forming a tubular core and preparing the same to have a material wound thereon, the steps of providing a tube-forming mandrel, winding strips of laminating material thereon to form a tube, providing a tube-supporting mandrel, removing the tube from said firstmentioned mandrel and telescoping the same about said supporting mandrel to support the same during the material-winding operation, said support mandrel having slightly smaller dimensions than said first-mentioned mandrel in a relation that necessitates said tube being pushed thereon in said telescoping operation.

2. In a method of forming a tubular core and preparing the same to have a material wound thereon, the steps of providing a tube-forming mandrel, forming a tube upon said mandrel, removing said tube after the formation thereof from said mandrel, providing a support mandrel having slightly smaller dimensions than said rstmentioned mandrel and being adapted to receive said tube thereon during the material-winding operation, and pushing said tube onto said support mandrel in preparation for having a material wound thereon, the dimensions of said support mandrel being related to the dimensions of said 5 tube and first-mentioned mandrel so that a push t between the tube and support mandrel is provided.

3. In a method of forming a coil support, the steps of providing a tube-winding mandrel, spirally winding strips of material thereon to form a tube, removing said tube from said winding mandrel, providing a support mandrel, the dimensions of said support mandrel being slightly smaller than the dimensions of said winding mandrel and matched therewith to provide a frictional resistance between said support mandrel and said tube, when said tube is telescoped about the support mandrel, resulting in a push tit therebetween, and pushing said tube onto said support mandrel in preparation for having a material wound thereon.

4. The method of claim 3 in which said mandrels are polygonal in cross section.

5. The method of claim 4 wherein said polygonal man drels are rectangular.

6. A method of forming a coil support, dimensionally accurate subsequent to a coil-winding operation wherein a wire coil is wound thereabout, comprising the steps of) providing a pair of matched mandrels of polygonal cross section, one of which is a tube-Winding mandrel and the other of which is a support mandrel having slightly smaller dimensions than said winding mandrel in a predetermined matched relation therewith, spirally win-ding strips of material about said winding mandrel to form a tube, saidl tube having slightly bowed side walls, removing said tube from said winding mandrel and pushing the same upon said support mandrel in preparation to having a wire coil wound thereabout, said matched mandrels being so related dimensionally that when said tube is pushed onto said support mandrel the corner portions of the tube and support mandrel meet in a snug engagement, and winding `a coil about the tube does not disturb the dimensional ac- `curacy thereof.

7, The method of claim 6 wherein the additional step is provided of winding a wire core upon said tube when it is received on said support mandrel.

8. A method of forming a coil having a hollow polygonal core ot predetermined internal dimensions, comprising the steps of spirally winding strips of material4 about a polygonal winding mandrel of preselected dimensions to form a hollow core, providing a polygonal support mandrel matched dimensionally with and to a slightly .smaller size than the winding mandrel so that the corners of the core snugly engage the corners of the support mandrel when the two are telescoped while permitting the core faces to bow outwardly slightly, positioning said core upon said support mandrel, and winding a coil about said core.

References Cited in the le of this patent UNITED STATES PATENTS 1,625,470 Jauch Apr. 19, 1927 1,625,471 Jauch Apr. 19, 1927 1,652,992 Krantz Dec. 13, 1927 2,274,681 Fletcher Mar. 3, 1942 2,343,096 Stahl Feb. 29, 1944 2,659,543 Guyer Nov. 17, 1953 

